The present invention relates generally to nozzle assemblies, and more particularly to fuel injectors having reverse acting needle valves.
In most fuel injectors, a needle valve opens inwardly to open the nozzle of the fuel injector to the combustion space. In a typical example, the nozzle valve member is biased toward its downward closed position in contact with the valve seat by a biasing spring. At the initiation of an injection event, high pressure fuel surrounds the valve member and acts on a lifting hydraulic surface of the valve member. When the pressure of the fuel reaches a valve opening pressure, the valve member can move upward, and thus farther inward, against the action of the biasing spring to open a fuel path from the fuel injector into the combustion space. Toward the end of an injection event, the biasing spring, which may or may not be assisted by a hydraulic closing force, pushes the needle back toward its closing position where it impacts the valve seat to close the nozzle outlet and end the injection event.
In most instances, the metal of the tip component where the nozzle valve seat is located is relatively thin and exposed directly to the hostile combustion space environment. Over its useful life, the needle valve member will impact its valve seat with relatively high loads many millions of cycles. In some instances, the impact load and fatigue stress caused by the closing of the needle valve can sometimes cause tip failures. When this occurs, extensive engine damage can occur because of loose metallic debris from the fuel injector failure finding its way into the combustion space. While these failures are extremely rare, the damage done to an engine can be so profound that engineers are often seeking ways in which the possibility of catastrophic engine damage can be eliminated and the instances of fuel injector nozzle assembly failures reduced.
The present invention is directed to overcoming one or more of the problems set forth above.
A nozzle assembly includes a tip body having a lower end and defining a nozzle outlet. A needle sleeve is at least partially positioned in the tip body and includes a valve seat. A needle valve member is at least partially positioned within the needle sleeve, and is moveable between a closed position in contact with the valve seat and an open position out of contact with the valve seat. The needle valve member moves toward the lower end of the tip body when moving toward its open position. The nozzle assembly finds its preferred application in hydraulically-actuated fuel injectors having direct control needle values.